The present invention relates to an information processing method for synthesizing main image information (which represents a portrait face image, for example) with sub image information (which is additional information, such as security information) and recording resultant synthetic image on a recording medium. The information processing method is also for sensing the sub image information from the recorded synthetic information.
In recent years, the technology for electronic watermark and signature is attracting more attention in accordance with the widespread computerization of information and the wide use of the Internet. This kind of technology creates synthetic image information by synthesizing main and sub image information. It is effective in preparing an ID card on which a portrait face image is printed, and also effective in preventing making an illegal copy, forgery, and modification of a picture in which copyright information is embedded.
“How To Synthesize And Encode Text Data In Color Density Pattern,” Journal Published by the Academic Image Electronics Society of Japan, 17-4 (1988), pp. 194-198, discloses a method for superimposing information on a digital image represented in pseudo-gradation.
Jpn. Pat. Appln. KOKAI Publication No. 9-248935 discloses a method for embedding a monochromatic binary image in a color image, using color sensitivity.
Jpn. Pat. Appln. KOKAI Publication No. 6-10190 discloses a method for preventing forgery and modification of an ID card. According to the reference, the ID card is overlaid with either a transparent film having a unique fine-line pattern or mesh pattern, or a lenticular film having a predetermined frequency. Since moiré patterns generated then are different depending upon the films laid on the ID card, the forgery and modification are prevented.
According to “How To Synthesize And Encode Text Data In Color Density Pattern,” the sub image information embedded in synthetic image information is reproduced for verification by reading the synthetic image information by use of high-resolution read means and reproducing the sub image information from the read image information. Since the high-resolution read means (scanner) is required for reading the synthetic image formation, the verification is not easy.
According to Jpn. Pat. Appln. KOKAI Publication No. 9-248935, the embedded sub image picture is reproduced by laying a sheet-like mask on the synthetic image information with high accuracy. In this case, the sub image information is reproduced by accurately positioning the sheet-like mask and the synthetic image information with reference to each other. In other words, extremely high accuracy is needed when the synthetic image information is recorded and when the sub image information is reproduced. Since easy reproduction of the sub image information is not enabled, easy verification is not possible.
According to Jpn. Pat. Appln. KOKAI Publication No. 6-10190, sub image information used for verification is prepared in a state where it can be visually perceived by a human being. This means that the storage position of the information that is essentially important to the verification may be easily known. Hence, the method of the reference is not reliable in terms of security.
As described above, the conventional information processing method has the problem that the easy verification based on the sub image information for security and the reliable security for verification are incompatible.